1. Field of the Invention
This invention relates to an improved method for ply-twisting nylon yarns at twisting speeds greater than 6000 rpm. More particularly, the invention involves coating the nylon fibers with less than about 1% by weight of finish containing an alkyl polyoxyalkylene carboxylate ester lubricant composition. The resulting ply-twisted yarn is especially suitable for use as pile in carpets.
2. Description of the Related Art
Typical carpets used in residences include loop pile and cut pile carpets. These carpets are made by inserting heat-set, ply-twisted pile yarn into a backing material. For loop pile carpets, the loops are not cut. For cut pile carpets, which are more common, the loops are cut to form substantially parallel vertical tufts.
The yarns which are used in such carpets are prepared by cable-twisting, or ply-twisting, two yarns together, and heat-setting them in their twisted condition. Problems in ply-twisting such yarns are discussed in Polejes, J. D., "Principles of Cable Twister Design and Operation", Canadian Textile Journal, September 1984, pp. 56-65.
Generally, a conventional apparatus for ply-twisting the yarns includes a means for feeding one yarn vertically upward from a stationary yarn supply package, located in a yarn supply bucket, and rotating another yarn around the first to form a twisted, combined yarn. The path of the rotating yarn is known as a "balloon". A guide, such as a fixed ring or jacket, is used for guiding and restricting the yarn in the balloon. As the yarn travels in the balloon, it comes into physical contact with the guide. These guides, or limiters, provide a means for controlling or limiting the extent and tension of the yarn in the balloon and are discussed in more detail in such patents as, Kresslein, U.S. Pat. No. 3,065,592, Nimtz et al., U.S. Pat. No. 3,094,835, and U.K. Patent 1,094,071.
A significant problem in using such conventional balloon guides is the high degree of friction created between the guides and the yarn in the balloon. While wind-up speeds are about 100 meters/minute, the speed of the threadline traversing the balloon limiter can exceed 10,000 meters/minute. This high speed contact between the balloon limiter and yarn results in generating polymer dust, broken filaments, deposits on the limiter, and irregular tension or breaks of the entire yarn. Furthermore, these problems become more pronounced as twisting speeds are raised to attain greater productivity of the twisting equipment.
Thus, a conventional solution for ply-twisting nylon bulked continuous filament (BCF) yarns has been developed. This process involves running the twisting equipment at a speed of at least about 6000 rpm, and applying sufficient finish to the supply yarns, so that the frictional problems with the balloon limiters are suppressed. The nylon yarns are coated with greater than 1% finish by weight, applied in either a one-step or two-step process.
In a one-step process, the total finish ("primary" or "spin" finish) is applied to the fibers during spinning, just after the fibers have substantially cooled and prior to such processes as drawing, crimping, wind-up, etc. In a two-step process, finish "A" (primary finish) is applied as in the one-step process, and finish "B" (secondary finish), which may be identical in composition to finish "A", is applied to the fibers after further processing such as drawing, crimping, etc., but before twisting.
These fiber finishes are normally composed of a mixture of lubricants and other chemical substances which impart specific properties to the fiber. Typical additives include, e.g., antistatic agents, antioxidants, and UV stabilizers. Emulsifiers are also often added in order to provide a stable finish which may more easily be applied to the fiber. Specific examples of conventional finishes used for ply-twisting nylon BCF yarns include emulsified coconut oil as disclosed in Champaneria et. al., U.S. Pat. No. 4,338,372, or water soluble lubricants, such as Methoxy PEG 400 Monopelargonate, available from Henkel Corp., as "Emery" 6724.
However, the application of such high amounts of finish is costly, and its presence on the yarn creates problems for the yarn user. If the carpet is washed as part of a dyeing or scouring process, the presence of the finish ingredients creates an environmental problem in the waste water disposal system of the carpet maker's locality. If the carpets are not washed as part of the carpet manufacturing process, the finish remains on the yarn, attracting and holding dirt.
In view of current environmental and economic concerns, it would be highly desirable to discover a method for ply-twisting nylon yarn satisfactorily on conventional twisting equipment having a speed greater than about 6000 rpm, without the need for conventional finish levels.